Wenyong Pan, Kris Innanen and Yu Geng

ABSTRACT

Seismic full-waveform inversion (FWI) methods hold strong, though still largely
un-tapped, potential to recover multiple subsurface elastic properties for hydrocarbon
reser-voir characterization. Simultaneously updating multiple physical parameters
introduces the problem of interparameter tradeoff, arising from the inherent ambiguities
between dif-ferent physical parameters, which increases nonlinearity and uncertainty of
multiparame-ter FWI. The coupling effects of different physical parameters are
significantly influenced by model parameterization and acquisition arrangement. An
appropriate choice of model parameterization is critical to successful field data
applications of multiparameter FWI. The objective of this paper is to examine the
performances of various model parameteri-zations in isotropic-elastic FWI with walk-away
vertical seismic profile (W-VSP) dataset for unconventional Heavy oil reservoir
characterization. Six model parameterizations are considered: velocity-density (α,
β and ρ'), modulus-density (κ, μ and ρ), Lamé-density (
λ, μ' and ρ'''), impedance-density (I
P
, I
S
and ρ''),
velocity-impedance-I (α', β' and I'
P
), and
velocity-impedance-II (α'', β'' and I'
S
). We begin analyzing the
interparameter trade-off with scattering radiation patterns for each of these
parameterizations, which is one common strategy for qualitative parameter resolution
studies in isotropic-elastic FWI. In this paper, we discuss the advantages and
limitations of the scattering radiation patterns for interparameter tradeoff analysis
and recommend to evaluate the interparameter trade-offs using interparameter
contamination kernels, which provide complete and quantitative measurements of the
interparameter contaminations and can be constructed efficiently with the adjoint-state
approach. Synthetic W-VSP isotropic-elastic FWI experiments verify our conclusions about
interparameter tradeoffs for various model parameterizations. Density profiles are most
strongly influenced by the interparameter contaminations; depending on model
parameterization, the inverted density profile can be over-estimated, under-estimated or
spatially distorted. The model parameterization, velocity-density, appears amongst the
six cases to provide stable and informative density features not included in the
starting model. Field data applications of multicomponent W-VSP isotropic-elastic FWI
were also carried out with various model parameterizations. The target Heavy oil
reservoir zone, characterized by low α-to-β ratios and low Poisson’s ratios,
can be identified clearly with the inverted isotropic-elastic parameters.